We have discovered VDJ beta and VJ alpha gene rearrangements in MS brain plaques that encode amino acid sequences identical to those seen in T cell clones from humans, mice and rats that have specificity for myelin basic protein (MBP) peptide 87-99. Using a high-efficiency expression system for TCR alpha and beta chains, we will rigorously prove that a major T cell response in the MS lesion is directed to MBPp87-99. We have developed potent T cell receptor antagonists for p87-99 that suppress ongoing paralysis in rodent models of EAE, and suppress proliferative and cytotoxic responses to p87-99 in humans. We will determine the putative contacts for amino acids in the TCR CDR3 regions with residues of p87-99. A core motif containing MBP87-91 (VHFFK) is found in this epitope. A number of microbes share sequence homology with this core motif-VHFFK, and stimulate MBPp87-99 specific T cells. We will determine whether microbial epitopes can trigger the transfected construct, as efficiently as the native MBP epitope. This would indicate how these T cells might become activated during infection, supporting the notion that self- reactivity arises from the molecular mimicry of self-antigens by microbes. Since T cells reactive to MBP p87-99 trigger EAE, we will test whether these microbial sequences either trigger EAE, or alternatively whether they serve as TCR or MHC antagonists and can block disease induction. Thus we will consider whether molecular mimics of MBP epitopes can induce disease or protect from pathology. We have demonstrated that a dominant antibody response found in the MS brain plaque and in MS cerebrospinal fluid is directed to an overlapping region of the MBP molecule from p86-99. This epitope is identical to the epitope restricted by HLA DR2 beta (HLA DRB1*1501), and overlaps with the epitope restricted by HLA DR2 alpha (HLA DRB5*0101). We will analyze immunoglobulin gene rearrangements in MS brain using RT-PCR, and in CSF using single cell PCR. We will see whether there are restricted Ig CDR3 motifs in MS. We will compare these CDR3 motifs to those found in murine monoclonal antibodies raised against the identical epitope p86-99. Our persistent goal is to develop selective immunotherapy for multiple sclerosis, a chronic disease of the central nervous system affecting approximately 250,000 Americans.